1. Field
One embodiment of the present invention relates to a disk drive, and in particular, to a servo writing technique using a spiral servo pattern.
2. Description of the Related Art
In general, in disk drives typified by hard disk drives, servo patterns (servo data) used for head positioning control are recorded on a disk medium that is a data recording medium. The disk drive uses the servo patterns read by the head to controllably place the head at a target position (target track) on the disk medium.
The servo patterns recorded on the disk medium have a plurality of servo sectors normally arranged circumferentially at a fixed interval so as to constitute concentric servo tracks. The disk drive positions the head on the basis of the servo patterns and uses the head to record user data on the disk medium to construct concentric data tracks.
The servo patterns are recorded on the disk medium by a servo write step included in a disk drive manufacturing process. A proposal has been made of a method of recording a spiral servo pattern constituting a base pattern on the disk medium during the servo write step (see, for example, U.S. Pat. No. 5,668,679).
In the servo write step in accordance with the proposed method, a spiral servo pattern is recorded, by, for example, a dedicated servo track writer (STW), on the disk medium not incorporated yet into a disk drive to be shipped as a product. Alternatively, a head in the drive itself records the spiral servo pattern.
The disk medium is subsequently incorporated into the disk drive, which performs a servo self-write method to write radial servo patterns (hereinafter referred to as specified servo patterns for convenience) used for the product to the disk medium. The specified servo patterns constitute the concentric servo tracks.
The servo self-write method enables the specified servo patterns to be written to the disk medium while moving the head of the disk drive, for example, from the inner periphery toward outer periphery of the disk medium, using the spiral base pattern pre-recorded on the disk medium as a base pattern.
The servo self-write step writes the specified servo patterns to the disk medium at specified positions by positioning the head of the disk drive on the basis of the spiral servo pattern. Only servo burst signals are recorded in the spiral servo pattern and not position data required to detect a radial position on the disk medium.
In actuality, the radial position (the position of a concentric track) is determined on the basis of the time elapsed since the head started moving from an end of the spiral servo pattern. That is, the servo self-write step adopts a method of gradually moving the head from the start position of the spiral servo pattern to place the head at a specified position and then writing the specified servo pattern to that position.
Such a method may fail to determine the radial position of the moving head if during a servo write operation, the write operation is stopped by an adverse effect, for example, a shock and then restarted.